In 1 1/2 quart casserole, combine onion and butter.
Microwave at high (10) 1 to 2 minutes until onion is tender.
Blend in cornstarch, pepper, cream, Worcestershire sauce and soy sauce.
Microwave at high (10) 2 to 3 minutes, until slightly thickened and bubbly, stirring every minute.
Add American cheese, cream cheese and parsley.
Microwave at high (10) 2 to 4 minutes, until cheese is melted and mixture is heated through, stirring every minute.